Photovoltaic Systems

Front 1

Photovoltaics is a solar energy technology that uses the unique properties of ______ to directly convert solar _______ into electricity.

Back 1

semiconductors
radiation

Front 2

Many advantages and benefits add value to PV systems beyond the potential _______.

Back 2

economic savings

Front 3

Photovoltaics is an environmentally friendly technology that causes no _____ or ______.

Back 3

noise
pollution

Front 4

Currently, the most significant disadvantage of PV systems is what?

Back 4

the high initial cost compared to prices for competing power-generating technologies.

Front 5

The photovoltaic effect was discovered long before it was just for the generation of ______.

Back 5

electricity

Front 6

Improvements in _____ efficiencies and ______ methods are reducing the cost of PV systems.

Back 6

cell
manufacturing

Front 7

_______ for conventional electricity-generating technologies help make PV and other renewable energy systems more cost-effective.

Back 7

Higher costs

Front 8

_____ applications were the first practical use of PV technology.

Back 8

Space

Front 9

PV systems are particularly well-suited for ______ and ______ applications.

Back 9

portable
remote

Front 10

______ power systems are the fastest-growing application of PV systems.

Back 10

Supplemental

Front 11

________ PV power plants are not yet common, but are being studied for future widespread use.

Back 11

Utility-scale

Front 12

There are many levels of ______ and _______ that support the PV industry.

Back 12

businesses
organizations

Front 13

______ installers are critical for quality installations and good _______ perception of the PV industry.

Back 13

Skilled
public

Front 14

______ renewable energy policies support further development and growth of the US PV industry.

Back 14

Government

Front 15

______ collectors absorb solar energy from many directions on a flat surface without concentrating it.

Back 15

Flat-plate

Front 16

______ collectors focus solar radiation from a large area onto a small area that contains special PV cells or heat-absorbing materials.

Back 16

Concentrating

Front 17

Integrating solar energy design techniques into architecture is an example of a _______ solar energy technology.

Back 17

passive

Front 18

Solar ______ energy is an efficient use of solar radiation that can be utilized in many ways.

Back 18

thermal

Front 19

Solar thermal energy can be converted into electricity, though only on a ______ scale that is impractical for ______ and ______ applications.

Back 19

large
residential
commercial

Front 20

Sunlight can be used for natural lighting in almost any indoor space by using ______.

Back 20

fiber optics

Front 21

Photovoltaics

Back 21

is a solar energy technology that uses the unique properties of certain semiconductors to directly convert solar radiation into electricity.

Front 22

Photovoltaic system

Back 22

is an electrical system consisting of a PV module array and other electrical components needed to convert solar energy into electricity usable by loads.

Front 23

Load

Back 23

a piece of equipment that consumes electricity.

Front 24

Utility

Back 24

a company that produces and/or distributes electricity to consumers in a certain region or state.

Front 25

Grid

Back 25

the utility's network of conductors, substations, and equipment that distributes electricity from its central generation point to the consumer.

Front 26

Distributed generation

Back 26

a system in which many smaller power-generating systems create electrical power near the point of consumption.

Front 27

Balance-of-system (BOS) component

Back 27

an electrical or structural component, aside from a major component, that is required to complete a PV system

Front 28

Integrator

Back 28

is a business that designs, builds, and installs complete PV systems for particular applications by matching components from various manufacturers.

Front 29

AHJ- Authority Having Jurisdiction

Back 29

an organization, office, or individual designated by local government with legal powers to administer, interpret, and enforce building codes

Front 30

Solar energy collector

Back 30

a device designed to absorb solar radiation and convert it to another form, usually heat or electricity.

Front 31

Flat-plate collector

Back 31

a solar energy collector that absorbs solar energy on a flat surface without concentrating it, and can utilize solar radiation directly from the sun as well as radiation that is reflected or scattered by clouds and other surfaces.

Front 32

Concentrating collector

Back 32

a solar energy collector that enhances solar energy by focusing it on a smaller area through reflective surfaces or lenses.

Front 33

CSP- Concentrating solar power

Back 33

a technology that uses mirrors and lenses to reflect and concentrate solar radiation from a large area onto a small area.

Front 34

What are the advantages of a PV system? (6)

Back 34

-If alternative power is very expensive, a PV system may save the consumer money
-Provides "green energy" with no noise or pollution.
-They are flexible and can be adapted to different applications
-Easy to expand for increased capacity.
-Very reliable and last a long time with minimal maintenance
- Offer energy independence (no utility power outages on a stand alone system)

Front 35

What are the disadvantages of a PV system? (6)

Back 35

-high initial cost
-require a large array area to produce significant power
-Not all locations are a good solar radiation source.
-Consumers have a lack of knowledge about the systems
-Many areas have little or no infrastructure for PV installation support.
-Many areas have few qualified installers available.

Front 36

What are the PV design priorities for Space applications?

Back 36

high efficiency and low weight (cost is least important)

Front 37

What are the PV design priorities for Portable applications?

Back 37

Must be light and mobile. They will need to be repositioned each time they are relocated. They are small and can only power modest loads. They may require a battery for nighttime operations.

Front 38

What are the PV design priorities for Remote applications?

Back 38

They must be large enough to handle the loads and may need to have a battery or generator back up for supplementation.

Front 39

What are some advantages to using PV technology to build utility-scale power plants?

Back 39

- PV systems produce power during the daylight hours when electricity demand is greatest, this increases value to the utility
-PV power plants can be built more quickly than conventional power plants due to it's simplicity.
-PV power plants can be located closer to populated areas (no noise, pollution)
-PV power plants can be expanded easily and incrementally as demand increases.

Front 40

What is the role of an integrator?

Back 40

Integrators work with homeowners, businesses, organizations, contractors, and utilities to design, install, monitor, and maintain PV systems. They also work with builders and architects to create aesthetically pleasing buildings using PV systems that meet local codes, standards, and regulations.

Front 41

How is installer training vital to the continued growth of the PV industry?

Back 41

To ensure that the installations are high quality and safe. Safe and quality PV system installations are essential for the success and acceptance of this technology. Installers are also the most visible members of the PV industry to the customers, making it vital that installers be professional and qualified.

Front 42

How are government policies being used to encourage development of renewable energy technologies?

Back 42

-through incentives such as grants, rebates, renewable energy credits, low/no interest loans, tax exemptions or credits, etc.
-through quotas such as requiring a certain percentage of electricity comes from renewable sources.

Front 43

Why are concentrating collectors more efficient than flat-plate collectors?

Back 43

Concentrating collectors have increased efficiency and reduced size because of the ability to channel more solar radiation onto the desired surface.

Front 44

The sun's radiant energy comes from _______ at its core.

Back 44

nuclear reactions

Front 45

Solar irradiance

Back 45

a measure of solar power per unit area

Front 46

Solar irradiation

Back 46

a measure of solar energy received on a surface over time.

Front 47

The solar constant is...

Back 47

the irradiance reaching Earth's atmosphere.

Front 48

Solar radiation is composed of....

Back 48

electromagnetic radiation in a range of wavelengths and in various amounts.

Front 49

The atmosphere ______ the amount of radiation that reaches Earth's surface and changes the ______ of the radiation.

Back 49

reduces
composition

Front 50

Peak sun

Back 50

the estimated maximum solar irradiance at Earth's surface.

Front 51

Name 3 things that can be used to measure solar irradiance.

Back 51

- Pyranometers
-Pyrheliometers
-reference cells

Front 52

Earth's tilt results in....

Back 52

changing solar position in the sky throughout the year.

Front 53

Solar time is based on....
and can differ significantly from....

Back 53

the sun's apparent motion (due to Earth's rotation).
standard time.

Front 54

Solar window

Back 54

the area of the sky encompassing the range of possible sun positions throughout the year for a particular location.

Front 55

What 3 things affect how much available solar radiation an array can utilize?

Back 55

- the type of array
- the orientation of the array
- the mounting configuration of the array

Front 56

What is the optimal orientation for maximum annual energy production of a flat-plate collector?

Back 56

an azimuth angle of due south and a tilt angle close to the latitude.

Front 57

What can solar radiation data be used to optimize?

Back 57

the performance of a PV system for a particular location, season, month, array type, array orientation, and mounting configuration.

Front 58

Radiation

Back 58

energy that emanates from a source in the form of waves or particles.

Front 59

extraterrestrial solar radiation

Back 59

solar radiation just outside Earth's atmosphere

Front 60

Electromagnetic radiation

Back 60

radiation in the form of waves with electric and magnetic properties

Front 61

electromagnetic spectrum

Back 61

the range of all types of electromagnetic radiation, based on wavelength

Front 62

total global radiation

Back 62

all the solar radiation reaching Earth's surface and is the sum of direct and diffuse radiation

Front 63

Direct radiation

Back 63

solar radiation directly from the sun that reaches Earth's surface without scattering

Front 64

Diffuse radiation

Back 64

solar radiation that is scattered by the atmosphere and clouds

Front 65

Zenith

Back 65

the poing in the sky directly overhead a particular location

Front 66

zenith angle

Back 66

the angle between the sun and the zenith

Front 67

(AM) air mass

Back 67

a representation of the relative thickness of atmosphere that solar radiation must pass through to reach a point on Earth's surface.

Front 68

Terrestrial solar radiation

Back 68

solar radiation reaching the surface of the Earth

Front 69

Peak sun hours

Back 69

the number of hours required for a day's total solar irradiation to accumulate at peak sun condition.

Front 70

insolation

Back 70

the solar energy that reaches Earth's surface over the course of a day.

Front 71

pyranometer

Back 71

a sensor that measures the total global solar irradiance in a hemispherical field of view.

Front 72

pyrheliometer

Back 72

a sensor that measures only direct solar radiation in the field of view of the solar disk (5.7 degrees)

Front 73

reference cell

Back 73

an encapsulated PV cell that outputs a known amount of electrical current per unit of solar irradiance.

Front 74

ecliptic plane

Back 74

the plane of Earth's orbit around the sun.

Front 75

equatorial plane

Back 75

the plane containing Earth's equator and extending outward into space

Front 76

solar declination

Back 76

the angle between the equatorial plane and rays of the sun.

Front 77

solstice

Back 77

Earth's orbital position when solar declination is at its minimum or maximum

Front 78

equinox

Back 78

Earth's orbital position when solar declination is zero

Front 79

Solar time

Back 79

a timescale based on the apparent motion of the sun crossing a local meridian

Front 80

meridian

Back 80

a plane formed by a due north-south longitude line through a location on Earth and projected out into space

Front 81

solar noon

Back 81

the moment when the sun crosses a local meridian and is at its highest position of the day

Front 82

solar day

Back 82

the interval of time between sun crossing of the local meridian, which is approximately 24 hr.

Front 83

standard time

Back 83

a timescale based on the apparent motion of the sun crossing standard meridians.

Front 84

Equation of Time

Back 84

the difference between solar time and standard time at a standard meridian

Front 85

analemma

Back 85

a diagram of solar declination against the Equation of Time

Front 86

solar altitude angle

Back 86

the vertical angle between the sun and the horizon

Front 87

solar azimuth angle

Back 87

the horizontal angle between a reference direction (typically due south in the Northern Hemisphere) and the sun

Front 88

array tilt angle

Back 88

the vertical angle between horizontal and the array surface

Front 89

array azimuth angle

Back 89

the horizontal angle between a reference direction and the direction an array surface faces.

Front 90

incidence angle

Back 90

the angle between the sun's rays and a line perpendicular to the array surface.

Front 91

single-axis tracking

Back 91

a sun tracking system that rotates one axis to approximately follow the position of the sun.

Front 92

Dual-axis tracking

Back 92

a sun tracking system that rotates two axes independently to exactly follow the position of the sun.

Front 93

What is the difference between irradiance and irradiation.

Back 93

irradiance is solar power per unit of area (usually watts per square meter)
irradiation is the total amount or solar energy accumulated on an area over time (usually units of watt-hours per square meter)

Front 94

Why is the solar constant specified for Earth's distance from the sun?

Back 94

In space, solar power remains relatively constant for a given distance from the sun because there is no atmosphere to scatter and absorb the energy.

Front 95

What is the difference between direct radiation and diffuse radiation?

Back 95

Direct radiation is solar radiation directly from the Earth's sun without scattering.
Diffuse radiation is solar radiation that has been scattered by the atmosphere and clouds.

Front 96

How are the solar constant and peak sun values similar and how do they differ?

Back 96

The solar constant is the average Extra-terrestrial solar irradiance at a distance of 1AU from the sun and have a value of about 1344 W per square meter.
The peak sun value is an estimate of maximum terrestrial solar irradiance around solar noon at sea level and is about 1000 W per square meter. One is a measurement just outside the atmosphere, the other is a measurement under the atmosphere. Both are approximate measurements of solar radiation at a particular location.

Front 97

What is the role of air mass in terrestrial solar radiation?

Back 97

Air mass is the amount of atmosphere that solar radiation must pass through to get to the Earth's surface. The more atmosphere, the more the radiation is scattered before getting to the surface.

Front 98

What is insolation?

Back 98

another term for solar radiation energy and is the solar irradiation received over a period of time, typically one day (kWh/square meter/day) or equivalent peak sun hours. Insolation is usually used to rate the solar energy potential of a location by calculating the average energy received on a surface per day (insolation maps).

Front 99

How can pyranometers be used to measure only direct solar radiation?

Back 99

The direct radiation measurement is calculated by subtracting the diffuse measurement from the global measurement.

Front 100

Explain how the solstices and equinoxes relate to the sun's apparent motion across the sky.

Back 100

A solstice is when the Earth's orbital position is at it's minimum or maximum causing all darkness or all daylight at either of the two poles.
An equinox is when the Earth's orbital position causes even day's and nights all over the world.

Front 101

Which two factors affect the difference between solar time and standard time?

Back 101

location and time of year.

Front 102

Which factors define the solar window?

Back 102

The solar window is the area of sky between the summer and winter sun paths for a particular location.

Front 103

Why does the optimal array tilt angle change throughout the year?

Back 103

Seasonal sun path changes and local climate variations may affect the optimal tilt angle for an array in a particular location. Longer days in the summer favor a smaller tilt angle for maximum annual energy gain, and if summer weather is very cloudy, a greater tilt angle may be favored to take advantage of clearer winter weather.

Front 104

How does the type of collector and mount affect the potential energy gain for an array?

Back 104

If the mount has tracking (single or dual) it can capture more solar gain (up to 40% more). Flat plate collectors can use direct and diffused solar radiation and concentrating collectors only use direct solar radiation.

Front 105

The installer must determine the customers ______ and ______ regarding the future PV system.

Back 105

requirements
wishes

Front 106

The installer should research the available solar resource to determine the optimal _______.

Back 106

array orientation

Front 107

The installer should consider the average _______ conditions and potential for ______.

Back 107

weather
severe weather

Front 108

The installer should investigate the local _____ and, when applicable, ______ requirements.

Back 108

building codes
utility interconnection

Front 109

Site surveys are conducted by ______, ________, ________ ,_______, and _______ all applicable site conditions related to a PV installation

Back 109

observing
photographing
measuring
documenting
diagramming

Front 110

Certain _____ is required to conduct a site survey and collect the necessary information

Back 110

equipment

Front 111

Potential array locations must have sufficient ______ for the estimated array area and an adequate ______.

Back 111

space
orientation

Front 112

Sun path calculators are a common method of conducting ______ analyses on potential array locations.

Back 112

shading

Front 113

Potential locations for the array and other equipment should be evaluated for what 3 things?

Back 113

accessibility
structural integrity
existing electrical infrastructure

Front 114

Adjustment for __________ is necessary to determine the direction of due south when using a magnetic compass.

Back 114

magnetic declination

Front 115

A site survey should include a ______ of the proposed array location and the surrounding structures and electrical equipment.

Back 115

sketch

Front 116

An ______ reveals magnitudes and patterns of energy use that can be useful when sizing PV systems.

Back 116

energy audit

Front 117

Energy ________________ can improve the value of a PV system by reducing overall energy requirements.

Back 117

conservation measures

Front 118

Some systems are sized according to an _______ requirement, while other systems are designed to comply with ______ and have energy production estimated from the size.

Back 118

energy production
constraints

Front 119

site survey

Back 119

a visit to the installation site to assess the site conditions and establish the needs and requirements for a potential PV system.

Front 120

magnetic declination

Back 120

the angle between the direction a compass needle points (magnetic north) and true geographic north

Front 121

sun path calculator

Back 121

a device that superimposes an image of obstructions on a solar window diagram for a given location.

Front 122

profile angle

Back 122

the projection of the solar altitude angle onto an imaginary plane perpendicular to the surface of an obstruction.

Front 123

energy audit

Back 123

a collection of information about a facility's or customer's energy use.

Front 124

How is the available solar resource for a particular location determined?

Back 124

Solar radiation resource information is available as data sets for specific locations, and provides average daily solar radiation for each month on various surfaces. Where no data exists for a certain area, that local resource can be estimated by comparing the data for the closest sites.

Front 125

What environmental concerns can dictate the materials, design, and placement of a PV system?

Back 125

humid and marine environments require special corrosion resistant materials
Flooding and storm surge possibilities require the equipment to be located high off the ground or be protected from water
Windstorms and seismic events require special structural support or flexibility

Front 126

What are some of the acceptable methods of fall protection?

Back 126

Fall protection can be in the form of equipment worn by a worker to reduce the potential for injury from fall (full-body harness), or precautions taken in the work area to prevent a fall (guardrails).

Front 127

How do desired output, module efficiency, and module density affect the required area of an array?

Back 127

The larger the desired output, the more modules you will need, the more efficient the modules are, the less modules you will need, and how closely the modules are spaced will affect the array area requirement.

Front 128

When might an optimal array orientation be southwest instead of due south?

Back 128

If the local climate is clearer during the later afternoon, or if peak energy used is later in the afternoon.

Front 129

Describe how magnetic declination is used to determine true south.

Back 129

On a compass, true south is found by subtracting the declination from the direction of magnetic south. Consult an up-to-date magnetic declination map to determine the value in your area.

Front 130

Why is shading analysis a critical part of a site survey and how does it affect potential array locations?

Back 130

Shading on solar thermal collectors reduces performance by an amount proportional to the level of shading. However, PV arrays are much more sensitive to shading. Depending on the magnitude and location of the shading, the reduction in output can be disproportionately higher than the percentage of array area shaded. In worst cases, even a 10 percent shading can cause the loss of most of the output. You may need to adjust the location of the array to avoid most if not all shading.

Front 131

What are some of the methods for conducting a shading analysis?

Back 131

Use of a sun path calculator
Use the altitude angle method
Use the profile angle method

Front 132

Describe some of the methods used to check for roof deterioration.

Back 132

Signs of deterioration differ for various types of roofs.
-asphalt shingles: brittleness, cracking, loss of granular coating, warping
- roof tiles: cracks, misalignment or flaking material
-metal roofing: loss of galvanized coating and rusting on steel roofs, corrosion and pitting on aluminum roofs.

Front 133

Describe the three general categories of energy conservation measures.

Back 133

building modifications: modifying a building or its design to reduce energy consumes or lost
Energy management: managing existing loads to reduce energy demand and waste
Load efficiency: replacing loads with newer and more efficient versions

Front 134

The primary component common to all PV systems is the ______

Back 134

PV array

Front 135

PV systems usually require means to _______ or ________ PV power so that it can be used efficiently by loads.

Back 135

store
condition

Front 136

Energy storage systems balance energy _______ and _______

Back 136

production
demand

Front 137

__________, particularly ________ types, are by far the most common means of energy storage in PV systems.

Back 137

Batteries
lead-acid

Front 138

Most PV systems require more battery capacity than can be supplied by a single battery, so batteries in PV systems are often ________ to form _______.

Back 138

connected together
battery banks

Front 139

Power conditioning components may be _________ devices or may be ______ into a single power conditioning unit.

Back 139

individual
combined

Front 140

______ convert DC power from battery systems or arrays to AC power for AC loads or export to the utility grid.

Back 140

Inverters

Front 141

______ manage the charging of batteries from a DC power source, typically a PV array.

Back 141

Charge controllers

Front 142

______ are used when an AC power source, such as the utility grid or an engine generator, is available to provide supplemental battery charging.

Back 142

Battery chargers

Front 143

Since a PV array produces DC power, DC loads are used in many PV applications to avoid what?

Back 143

having to change the power to AC, this simplifies the system

Front 144

________ components are all of the remaining electrical and mechanical components needed to integrate and assemble the major components in a PV system.

Back 144

Balance-of-system (BOS)

Front 145

Besides the PV array, the ________________ is the most common source of electricity connected to PV systems

Back 145

electric utility grid

Front 146

Other electrical systems may be __________ with PV systems as additional sources of electricity, depending on the type of system and application requirements.

Back 146

interfaced

Front 147

_____________ PV systems are most popular for meeting small to medium sized electrical loads and are extensively used in remote off-grid areas or where extending the utility service is cost-prohibitive or impossible.

Back 147

Stand-alone

Front 148

In _______ PV systems, the output of a PV module or array is directly connected to a DC load.

Back 148

direct-coupled

Front 149

A _______ PV system consists of only an array, battery, and load.

Back 149

self-regulated

Front 150

Whenever loads are variable or uncontrolled, ______ is required to prevent damage to the battery from overcharge or over-discharge.

Back 150

charge control

Front 151

______ systems operate in parallel with and are connected to the electric utility grid.

Back 151

Utility-interactive

Front 152

______ systems can operate in either utility-interactive or stand-alone mode and use battery storage.

Back 152

Bimodal

Front 153

______ systems include an energy source other than an array and do not interact with the utility.

Back 153

Hybrid

Front 154

Common energy sources used in hybrid systems include... (3)

Back 154

engine generators
wind turbines
micro-hydroelectric generators

Front 155

battery bank

Back 155

a group of batteries connected together with series and parallel connections to provide a specific voltage and capacity.

Front 156

PCU-power conditioning unit

Back 156

a device that includes more than one power conditioning function.

Front 157

inverter

Back 157

a device that converts DC power to AC power

Front 158

charge controller

Back 158

a device that regulates battery charge by controlling the charging voltage and/or current from a DC power source, such as a PV array.

Front 159

rectifier

Back 159

a device that converts AC power to DC power

Front 160

charger

Back 160

a device that combines a rectifier with filters, transformers, and other components to condition DC power for the purpose of battery charging.

Front 161

DC-DC converter

Back 161

a device that converts DC power from one voltage to another

Front 162

MPPT-maximum power point tracker

Back 162

a device or circuit that uses electronics to continually adjust the load on a PV device under changing temperature and irradiance conditions to keep it operating at its maximum power point.

Front 163

engine generator

Back 163

a combination of an internal combustion engine and a generator mounted together to produce electricity.

Front 164

generator

Back 164

a device that converts mechanical energy into electricity by means of electromagnetic induction.

Front 165

gas turbine

Back 165

a device that compresses and burns a fuel-air mixture, which expands and spins a turbine.

Front 166

turbine

Back 166

a bladed shaft that converts fluid flow into rotating mechanical energy.

Front 167

UPS- uninterruptible power supply

Back 167

a battery-based system that includes all that additional power conditioning equipment, such as inverters and chargers, to make a complete, self-contained power source.

Front 168

wind turbine

Back 168

a device that harnesses wind power to produce electricity.

Front 169

micro-hydroelectric turbine

Back 169

a device that produces electricity from the flow and pressure of water.

Front 170

fuel cell

Back 170

an electrochemical device that uses hydrogen and oxygen to produce DC electricity, with water and heat as byproducts

Front 171

electrolyzer

Back 171

an electrochemical device that uses electricity to split water into hydrogen and oxygen

Front 172

stand-alone PV system

Back 172

a type of PV system that operates autonomously and supplies power to electrical loads independently of the electric utility.

Front 173

direct-coupled PV system

Back 173

a type of stand-alone system that uses no active control systems to protect the battery, except through careful design and component sizing.

Front 174

self-regulating PV system

Back 174

a type of stand-alone system that uses no active control systems to protect the battery, except through careful design and component sizing.

Front 175

utility-interactive system

Back 175

a PV system that operates in parallel with and is connected to the electric utility grid.

Front 176

net metering

Back 176

a metering arrangement where any excess energy exported to the utility is subtracted from the amount of energy imported from it.

Front 177

dual metering

Back 177

the arrangement that measures energy exported to and imported from the utility grid separately

Front 178

islanding

Back 178

the undesirable condition where a distributed-generation power source, such as a PV system, continues to transfer power to the utility grid during a utility outage

Front 179

bimodal system

Back 179

a PV system that can operate in either utility-interactive or stand-alone mode and uses battery storage.

Front 180

hybrid system

Back 180

a stand-alone system that includes two or more distributed energy sources.

Front 181

DC bus hybrid system

Back 181

a hybrid system that combines DC power output from all energy sources, including the PV array, for charging the battery bank.

Front 182

AC bus hybrid system

Back 182

a hybrid system that supplies the loads with AC power from multiple energy sources.

Front 183

Why is energy storage needed in most PV systems?

Back 183

so that it can be used effectively by electrical loads. Demand can fluctuate considerable and the output of most power generation technologies tends to be steadier or limited to certain times of the day, which means that an electricity supply does not always coincide with when it is needed.

Front 184

The voltage of PV modules varies somewhat with ________.

Back 184

temperature

Front 185

The current of PV modules varies proportionately to ________.

Back 185

solar irradiance

Front 186

Besides energy storage, what advantages do battery systems provide?

Back 186

In addition to energy storage, batteries provide short surge currents for loads with special starting requirements, which PV modules (as current-limited power sources) cannot provide. Most importantly batteries establish a stable system operating voltage, which allows the array to be optimized for maximum power and electrical loads (or inverters) to operate at their rated voltage.

Front 187

What is the difference between an inverter and a power conditioning unit?

Back 187

An inverter simply converts DC power to AC power. A PCU (power conditioning unit) is a device that includes more than one conditioning function (this includes inverter, DC-DC converters, power quality equipment, charge controllers, rectifiers, etc.)

Front 188

Explain the difference between a charge controller and a charger.

Back 188

A charge controller is a device that regulates battery charge by controlling the charging voltage and/or current from a DC power source (PV array). A charger is a device that conditions DC power for the purpose of battery charging (such as from AC power sources like the utility or a generator) to supplement battery charging.

Front 189

How does a maximum power point tracker maximize array output?

Back 189

For any combination of temperature and irradiance, there is a maximum possible power output that corresponds to a certain voltage and current. A MPPT circuit monitors array conditions and dynamically changes its resistance or input voltage to maximize power from an array.

Front 190

Which types of electrical energy sources are typically integrated with PV systems? (7)

Back 190

The electric utility grid
engine generators
gas-turbine generators
UPS-uninterruptible power supplies
wind turbines
micro-hydroelectric turbines
fuel cells

Front 191

Why is system sizing critically important for stand-alone PV systems?

Back 191

Since the size and cost of any stand-alone system is related to the magnitude and duration of the electrical load and the solar resource, energy efficiency is critical. You want the system to be large enough to handle the highest loads with the lowest insolation and in be able to safely charge any batteries without wasting energy or causing a dangerous overcharge situation.

Front 192

Compare the different types of stand-alone PV systems (3).

Back 192

Direct-coupled- the PV module or array is connected directly to the load. Because PV output varies with irradiance, the load must also be capable of operating over a range of voltages and be needed only when energy is available.
Self- Regulated- includes storage buy uses no active control systems to protect the battery, except through careful design and component sizing. The battery typically must be dramatically oversized to protect it from overcharge.
Charge-controlled- A charge controller will interrupt or redirect the charging of the battery in case of overcharging and remove loads in case of over discharging.

Front 193

Explain the ways in which interactive inverters interface with the utility grid. (2)

Back 193

net metering- the utility's electricity meter runs backwards when power is exported from the PV system to the utility. Under this arrangement, excess energy exported to the utility is subtracted from the amount of energy imported from it. Energy supplied to the utility is effectively credited to the customer at full retail value.
dual metering- is the arrangement that measures energy exported to and imported from the utility grid separately. This arrangement allows energy delivered to the consumer to be billed at full retail value, while power delivered to the utility is credited at a lower wholesale vale, the cost the utility pays to generate or purchase energy.

Front 194

How can bimodal systems be used to lower electricity costs when utility rates vary by time of day?

Back 194

A bimodal inverter can be programmed to supply the loads with energy from the array and battery bank during peak times, avoiding or minimizing the use of high-priced utility electricity. During off-peak times, the loads can be powered and the battery bank charged with less-expensive utility electricity.

Front 195

Compare the advantages and disadvantages of hybrid systems.

Back 195

advantages: greater system reliability and flexibility in meeting variable loads, may reduce total system costs.
disadvantages: complex in terms of equipment, system design and installation.

Front 196

_____ striking a PV cell give electrons the energy to move freely, which ______ the flow of electrical current.

Back 196

photons
induces

Front 197

Many materials can be made into PV cells, but _______ is currently the most common and economical material.

Back 197

crystalline silicon

Front 198

Silicon wafers can be made with ______, _______, or ______ silicon methods

Back 198

monocrystalline
polycrystalline
ribbon

Front 199

The ______ illustrates the basic electrical parameters and characteristics of PV devices.

Back 199

I-V curve

Front 200

The _______ is the operating point at which the PV device produces the most power and is the most efficient.

Back 200

maximum power point

Front 201

The ______ of the PV material and the _______ in the PV system affect the shape of the I-V curve.

Back 201

inherent properties
resistances

Front 202

______ and _______ affect the magnitude and position of the I-V curve.

Back 202

solar irradiance
cell temperature

Front 203

Any single I-V curve represents only one set of ______ for solar irradiance and cell temperature.

Back 203

conditions

Front 204

Cell temperature is influenced by 5 things.....

Back 204

-ambient temperature
-wind speed
-solar irradiance
-thermal characteristics of the device's packaging
-the way the cell or module is installed or mounted

Front 205

I-V curve parameters can be translated from reference irradiance and temperature conditions to other conditions through...

Back 205

the use of equations.

Front 206

PV cells are integrated electrically and mechanically to build ___________. Modules are integrated electrically and mechanically to build __________.

Back 206

modules
arrays

Front 207

The electrical concepts used to build voltage and current though series and parallel connections are ______ from cells to arrays.

Back 207

scalable

Front 208

____________ protect PV devices from damage and excessive loss of power by directing current around shaded or damaged devices.

Back 208

bypass diodes

Front 209

Standard test conditions are used with ________ so that modules can be compared effectively.

Back 209

performance figures

Front 210

Various standard test conditions have been developed in efforts to more realistically estimate module ________ in real-world situations.

Back 210

performance

Front 211

photovoltaic cell

Back 211

a semiconductor device that converts solar radiation into direct current electricity.

Front 212

semiconductor

Back 212

a material that can exhibit properties of both an insulator and a conductor

Front 213

Doping

Back 213

a process of adding small amounts of impurity elements to semiconductors to alter their electrical properties.

Front 214

p-type semiconductor

Back 214

a semiconductor that has electron voids

Front 215

n-type semiconductor

Back 215

a semiconductor that has free electrons

Front 216

photovoltaic effect

Back 216

the movement of electrons within a material when it absorbs photons with energy above a certain level.

Front 217

photon

Back 217

a unit of electromagnetic radiation

Front 218

p-n junction

Back 218

the boundary of adjacent layers of p-type and n-type semiconductor materials in contact with one another

Front 219

multi-junction cell

Back 219

a cell that maximizes efficiency by using layers of individual cells that each respond to different wavelengths of solar energy

Front 220

thin-film module

Back 220

a module-like PV device with its entire substrate coated in thin layers of semiconductor material using chemical vapor deposition techniques, and then laser-scribed to delineate individual cells and make electrical connections between cells.

Front 221

photoelectrochemical cell

Back 221

a cell that relies on chemical processes to produce electricity from light, rather than using semiconductors.

Front 222

wafer

Back 222

a thin, flat disk or rectangle of base semiconductor material

Front 223

monocrystalline wafer

Back 223

a silicon wafer made from a single silicon crystal grown in the form of a cylindrical ingot

Front 224

polycrystalline wafer

Back 224

a silicon wafer made from a cast silicon ingot that is composed of many silicon crystals.

Front 225

ribbon wafer

Back 225

a silicon wafer made by drawing a thin strip from a molten silicon mixture

Front 226

current-voltage (I-V) characteristic

Back 226

the basic electrical output profile of a PV device

Front 227

I-V curve

Back 227

the graphic representation of all possible voltage and current operating points for a PV device at a specific operating condition

Front 228

open-circuit voltage (Voc)

Back 228

the maximum voltage on an I-V curve and is the operating point for a PV device under infinite load or open-circuit condition, and no voltage output.

Front 229

short-circuit current (Isc)

Back 229

the maximum current on an I-V curve and is the operating point for a PV device under no load or short-circuit condition, and no voltage output

Front 230

maximum power point (Pmp)

Back 230

the operating point on an I-V curve where the product of current and voltage is at maximum

Front 231

maximum power voltage (Vmp)

Back 231

the operating voltage on an I-V curve where the power output is at maximum

Front 232

maximum power current (Imp)

Back 232

the operating current on an I-V curve where the power output is at maximum

Front 233

fill factor (FF)

Back 233

the ratio of maximum power to the product of the open-circuit voltage and short-circuit current.

Front 234

Efficiency

Back 234

the ratio of power output to power input

Front 235

family of I-V curves

Back 235

a group of I-V curves at various irradiance levels

Front 236

temperature-rise coefficient

Back 236

the coefficient for estimating the rise in cell temperature above ambient temperature due to solar irradiance.

Front 237

temperature coefficient

Back 237

the rate of change in voltage, current, or power output from a PV device due to changing cell temperature.

Front 238

module

Back 238

a PV device consisting of a number of individual cells connected electrically, laminated, encapsulated, and packaged into a frame.

Front 239

array

Back 239

a complete PV power-generating unit consisting of a number of individual electrically and mechanically integrated modules with structural supports, trackers, or other components.

Front 240

reverse bias

Back 240

the condition of a OV device operating at negative (reverse) voltage

Front 241

bypass diode

Back 241

a diode used to pass current around, rather than through, a group of PV cells

Front 242

breakdown voltage

Back 242

the minimum reverse-bias voltage that results in a rapid increase in current though an electronic device

Front 243

standard test conditions (STC)

Back 243

The most common and internationally accepted set of reference conditions, and rates module performance at a solar irradiance of 1000 W/m2, spectral conditions of AM1.5, and a cell temperature of 25C (77F).

Front 244

standard operating conditions (SOC)

Back 244

a set of reference conditions that rates module performance at a solar irradiance of 1000 W/m2, spectral conditions of AM1.5, and at a nominal operating cell temperature

Front 245

Nominal operating cell temperature (NOCT)

Back 245

a reference temperature of an open-circuited module based on an irradiance level of 800 W/m2, ambient temperature of 20C (68F), and wind speed of 1 m/s

Front 246

nominal operating conditions (NOC)

Back 246

a set of reference conditions that rates module performance at a solar irradiance of 800 W/m2, spectral conditions of AM1.5, and at a nominal operating cell temperature.

Front 247

PVUSA test conditions (PTC)

Back 247

a set of reference conditions that rates module performance at a solar irradiance of 1000 W/m2, ambient temperature of 20C (68F), and wind speed of 1 m/s

Front 248

Describe the basic process of manufacturing PV cells (6 steps)

Back 248

- the wafers are dipped in a sodium hydroxide solution to etch the surface and remove imperfections.
- they are then placed on racks and into a diffusion furnace where phosphorous gas penetrates the outer surfaces of the cell, creating a thin n-type semi-conductor layer surrounding the original p-type.
-the edge of the wafer is abraded to remove the n-type material
- antireflective coatings are then applied to reduce reflected sunlight and improve cell efficiency
- after the coatings dry, grid patterns are screen printed to the top surface of the cell with silver paste to provide a point for electron collection and connection to other cells
-the entire back surface of the cell is coated with a thin layer of metal (typically aluminum) which alloys with the silicon and neutralizes the n-type semiconductor layer on the back surface.

Front 249

Explain the relationships between PV cells, modules, panels and arrays.

Back 249

Individual PV cells are the basic building blocks for modules, several modules may be connected together to form a panel, modules (or panels) are in turn the building blocks for arrays and then complete PV systems.

Front 250

How does the photovoltaic effect limit the short-circuit current in PV devices?

Back 250

A short-circuited PV device will flow current only up to a certain point, because the electrons making up the current are not free to flow unless they are released by photons. The number of photons striking the PV is finite, and only some of those photons transfer enough energy to free an electron. Therefore the current flow cannot exceed the supply of free electrons. Only greater irradiance can increase the short-circuit current.

Front 251

Which methods can be used to estimate or calculate the maximum power point on an I-V curve?

Back 251

The maximum power point is located on the knee of the I-V curve and is typically 70-80% of the open-circuit voltage and 90% of the value of the short-circuit current. Maximum power voltage and current can be measured only while the PV device is connected to a load that operates the device at maximum power. Alternatively, the maximum power voltage and current can be determined from I-V curve data by multiplying each I-V pair and determining which pair results in maximum power.

Front 252

How does PV device efficiency affect required device area?

Back 252

Cells with higher efficiencies require less surface area to produce each watt of power.

Front 253

What effects do series and shunt resistance have in PV systems?

Back 253

Series resistance in PV devices includes the resistance of a cell, its electrical contacts, module interconnections, and system wiring. Increasing series resistance reduces the voltage over the I-V curve and decreases the maximum power output.
Shunt (parallel) resistance accounts for leakage currents within a cell, module, or array. This has an effect on an I-V curve opposite the effect of series resistance. It does not affect short-circuit current, however it reduces fill-factor and efficiency (lowering maximum voltage, current and power). Decreasing shunt resistance can indicate ground faults or short circuits within the array.

Front 254

Describe how varying solar irradiance affects the I-V characteristics of a PV device.

Back 254

Changes in solar irradiance have a small effect on voltage but a significant effect on the current output of PV devices. The current of a PV device increases proportionally with increasing solar irradiance. Consequently, since the voltage remains nearly the same, the power also increases proportionally.

Front 255

Describe how varying temperature affects the I-V characteristics of a PV device.

Back 255

For most types of PV devices, high operating temperatures significantly reduce voltage output and slightly increases current, this results in a net decrease in power.

Front 256

How are cells electrically connected to produce a module with desired voltage and current parameters?

Back 256

Individual cells are connected in series to create a desired voltage. Parallel connections are not generally used for individual PV devices, especially cells, but for series strings of cells and modules.

Front 257

What is the voltage and current resulting from series or parallel connections of dissimilar PV devices.

Back 257

Current values must be the same when connecting in series. Current values can be different when hooking up in parallel. Voltage does not affect power output whether hooked up in series or parallel, the voltage output of the series circuit equals the sum of the voltages of the individual devices and is the average voltage of all the devices when in parallel.

Front 258

How do bypass diodes protect modules from damage and preserve power performance?

Back 258

A reverse-biased device (shading or short circuit) will continue to pass current, but since the voltage is negative, the device will consume power instead of producing power. A bypass diode is used to pass current around, rather than through, a group of PV cells. The current is allowed to pass around groups of cells that are shaded or develop an open-circuit preventing an interruption of the continuity of the string. Without a bypass diode, reverse voltage may decrease until the breakdown voltage is reached, causing high currents and possible damage.

Front 259

Why is it important to understand the test conditions used in a module performance evaluation?

Back 259

Since so many variables affect the performance of a PV system, it is important to understand the test conditions used to evaluate performance so that realistic predictions can be made about actual system performance.

Front 260

_______ are collections of electrochemical cells electrically connected together in series.

Back 260

Batteries

Front 261

Electrochemical reactions produce a flow of electrons from the ___________ terminals to the ____________ terminals of a cell.

Back 261

negative
positive

Front 262

Physical factors affecting battery capacity include 3 things:

Back 262

1- the quantity of active material
2- the number, design and dimensions of the plates
3- the electrolyte concentration

Front 263

Operational factors affecting battery capacity include 5 things:

Back 263

1- discharge rate
2- charging method
3- temperature
4- age
5- condition of the battery

Front 264

Discharging and charging rates for a battery are based on what?

Back 264

the amount of charge applied in one hour

Front 265

Charging is done by applying an electrical current to the cell or battery in a direction ________ to the discharge. In order for the battery to accept current, the voltage of the charging source must be ____________ than the battery voltage.

Back 265

opposite
higher

Front 266

State of charge is .....
Depth of discharge is.....

Back 266

the available capacity within a battery
the capacity that has been removed

Front 267

Bulk charging.....
Absorption charging.....

Back 267

quickly charges up a battery to regulation voltage
slowly completes a battery charge

Front 268

_______________ is a controlled overcharge that ensures that each cell is fully charged.

Back 268

Equalization

Front 269

Overcharging a battery causes....

Back 269

water in the electrolyte to form gases, which escape though cell vents.

Front 270

Water lost from gassing of open-vent batteries must be....

Back 270

replaced

Front 271

Water lost from gassing of sealed or captive-electrolyte batteries....

Back 271

cannot be replenished

Front 272

____________ can have significant effects on capacity, electrolyte specific gravity, self-discharge, gassing voltage, voltage set points, and battery life.

Back 272

Temperature

Front 273

The concentration, or specific gravity, of the electrolyte can indicate what two things?

Back 273

1- the state of charge
2- general health of a cell

Front 274

_____________ and ________________ are common battery problems that can decrease battery performance and life.

Back 274

sulfation
stratification

Front 275

Uncontrolled charging and discharging can result in....

Back 275

loss of battery capacity and life

Front 276

The most common batteries used for PV applications are ___________ batteries

Back 276

traction

Front 277

Electrolytes can be in two forms:

Back 277

1- free-flowing liquid (flooded)
2- immobilized (captive)

Front 278

____________ batteries are highly suitable for most PV applications buy usually require a lot of maintenance.

Back 278

Lead-acid

Front 279

Some ____________ batteries are suitable for most PV applications and have good temperature tolerance buy can be expensive and difficult to maintain.

Back 279

nickel-cadmium

Front 280

Required battery bank voltage is often determined by ......

Back 280

load or inverter input voltage requirements

Front 281

Most PV systems with batteries operate at what voltages?

Back 281

12V, 24V, or 48V

Front 282

Batteries can be connected in series and parallel combinations to produce what?

Back 282

a desired system voltage level and capacity

Front 283

It is generally recommended that batteries be connected in as few ______ strings as possible.

Back 283

parallel

Front 284

Electrical codes and safety standards generally require batteries to be installed in an enclosure separated from....

Back 284

controls or other PV system components.

Front 285

Battery

Back 285

a collection of electrochemical cells that are contained in the same case and connected together electrically to produce a desired voltage.

Front 286

battery cell

Back 286

the basic unit in a battery that stores electrical energy in chemical bonds and delivers this energy through chemical reactions.

Front 287

plate

Back 287

an electrode consisting of active material supported by a grid framework.

Front 288

active material

Back 288

the chemically reactive compound on a battery cell plate.

Front 289

grid

Back 289

a metal framework that supports the active material of a battery cell and conducts electricity.

Front 290

Electrolyte

Back 290

the conducting medium that allows the transfer of ions between battery cell plates.

Front 291

Steady-state

Back 291

an open-circuit condition where essentially no electrical or chemical changes are occurring.

Front 292

open-circuit voltage

Back 292

the voltage of a battery or cell when it is at steady-state.

Front 293

Capacity

Back 293

the measure of the electrical energy storage potential of a cell or battery.

Front 294

Discharging

Back 294

the process of a cell or battery converting chemical energy to electrical energy and delivering current.

Front 295

cutoff voltage

Back 295

the minimum battery voltage specified by the manufacturer that establishes the battery capacity at a specific discharge rate.

Front 296

state of charge (SOC)

Back 296

the percentage of energy remaining in a battery compared to the fully charged capacity.

Front 297

depth of discharge (DOD)

Back 297

the percentage of withdrawn energy in a battery compared to the fully charge capacity.

Front 298

allowable depth of discharge

Back 298

the maximum percentage of total capacity that is permitted to be withdrawn from a battery.

Front 299

average daily depth of discharge

Back 299

the average percentage of the total capacity that is withdrawn from a battery each day.

Front 300

autonomy

Back 300

the amount of time a fully charged battery system can supply power to system loads without further charging

Front 301

self-discharge

Back 301

the gradual reduction in the state of charge of a battery while at steady-state condition.

Front 302

cycle

Back 302

a battery discharge followed by a charge

Front 303

charging

Back 303

the process of a cell or battery receiving current and converting the electrical energy into chemical energy.

Front 304

gassing voltage

Back 304

the voltage level at which battery gassing begins

Front 305

bulk charging

Back 305

battery charging at a relatively high charge rate that charges the battery up to a regulation voltage, resulting in a state of charge of about 80% to 90%

Front 306

Absorption charging

Back 306

battery charging following bulk charging that reduces the charge current to maintain the battery voltage at a regulation voltage for a certain period.

Front 307

Float charging

Back 307

battery charging at a low charge rate that maintains full battery charge by counteracting self-discharge.

Front 308

Equalizing charging

Back 308

current-limited battery charging to a voltage higher than the bulk charging voltage, which brings each cell to a full state of charge.

Front 309

Gassing

Back 309

the decomposition of water into hydrogen and oxygen gases as a battery charges.

Front 310

Overcharge

Back 310

the ratio of applied charge to the resulting increase in battery charge

Front 311

specific gravity

Back 311

the ratio of the density of a substance to the density of water

Front 312

sulfation

Back 312

the growth of lead sulfate crystals on the positive plate of a lead-acid cell

Front 313

Stratification

Back 313

a condition of flooded lead-acid cells in which the specific gravity of the electrolyte is greater at the bottom than at the top

Front 314

primary battery

Back 314

a battery that can store and deliver electrical energy but cannot be recharged.

Front 315

secondary battery

Back 315

a battery that can store and deliver electrical energy and can be charged by passing a current through it in an opposite direction to the discharging current.

Front 316

traction battery

Back 316

a class of battery designed for repeated deep-discharge cycle service

Front 317

starting, lighting, and ignition (SLI) battery

Back 317

a class of battery designed primarily for shallow-discharge cycle service

Front 318

stationary battery

Back 318

a class of battery designed for occasional deep-discharge limited-cycle service.

Front 319

flooded electrolyte

Back 319

electrolyte in the form of liquid

Front 320

catalytic recombination cap (CRC)

Back 320

a vent cap that reduces electrolyte loss from an open-vent flooded battery by recombining vented gases into water.

Front 321

catalyst

Back 321

a substance that causes other substances to chemically react but does not participate in the reaction.

Front 322

captive electrolyte

Back 322

electrolyte that is immobilized

Front 323

hybrid battery

Back 323

a battery that uses a combination of plate designs to maximize the desirable characteristics of each.

Front 324

battery bank

Back 324

a group of batteries connected together with series and parallel connections to provide a specific voltage and capacity.

Front 325

What is the difference between a battery and a cell?

Back 325

Batteries are collections of cells. Cells can be configured into batteries.

Front 326

Describe the chemical reactions that take place when a load or conductor is connected to the positive and negative terminals of a battery.

Back 326

At that moment, a chemical reaction begins that causes electrons to flow from the negative terminal to the positive terminal. At the negative terminal, the active material in the negative plate reacts with the electrolyte to form a new material that releases excess electrons. At the positive terminal, the active material in the positive plate reacts with the electrolyte to form a new material, which requires extra electrons to complete the reaction. When the battery is discharging, the excess electrons at the negative terminal are conducted outside the battery, through the load, to the positive terminal to complete the reactions at the positive plate.

Front 327

What 3 physical factors affect the capacity of a cell or battery?

Back 327

1- the quantity of active material
2- the number, design and dimensions of the plates
3- the electrolyte concentration

Front 328

What 5 operational factors affect the capacity of a cell or battery?

Back 328

1- discharge rate
2- charging method
3- temperature
4- age
5- condition of the cell or battery

Front 329

Explain the relationships between electrolyte specific gravity, freezing point, and state of charge (SOC).

Back 329

The state of charge is the percentage of energy remaining in a battery compared to the fully charged capacity. The electrolyte in a fully charged lead-acid battery is a solution of apx. 25% sulfuric acid and 75% water. Ions from the acid are consumed by the active material during discharging and released during charging, so the concentration of the acid in the water changes with state of charge. Concentrated sulfuric acid has a very low freezing point (-94F) while water has a higher freezing point (32F). Therefore, the freezing point of the electrolyte also varies with the specific gravity of the electrolyte. As the battery becomes discharged, the specific gravity decreases, resulting in a higher freezing point for the electrolyte.

Front 330

Why are traction batteries ideal for most PV applications?

Back 330

Traction batteries have fewer plates per cell than other types of batteries, but the plates are thick and durable. They are very popular in PV systems for their deep-cycle capability, long life, and durability.

Front 331

What are 4 relative advantages of captive-electrolyte batteries?

Back 331

1- spill-proof
2- easily transported
3- less susceptible to freezing
4- no need to replenish water (less maintenance)

Front 332

What are 2 relative disadvantages of captive-electrolyte batteries?

Back 332

1- can not be replenished
2- intolerant of excessive overcharge

Front 333

What are the 3 classifications of secondary batteries? What are these classes based on?

Back 333

1- Traction batteries
2- (SLI) Starting, Lighting and Ignition batteries
3- Stationary batteries
- the classes are based on discharge and cycle characteristics

Front 334

How does average daily DOD affect autonomy?

Back 334

They use the average daily DOD to determine what size battery bank is required to give a proper amount of autonomy (how long the system can supply power without further charging) for the PV system. If you have a higher load during times of the year where seasonal insolation is low, you may need a bigger battery bank. A battery bank is usually sized for 2-6 days of autonomy.

Front 335

How does discharge rate affect battery capacity?

Back 335

Capacity is directly affected by the rate of discharge. Lower discharge rates are able to remove more energy from a battery before it reaches the cutoff voltage. Higher discharge rates remove less energy before the battery reaches the same voltage.

Front 336

How can series and parallel combinations be used to design a battery system with a specific voltage and capacity?

Back 336

When hooking up batteries in series (+ to 1), the voltage adds up however the (current) capacity remains the same. When hooking up batteries in parallel (+ to +; - to -), the voltage remains the same, but the (current) capacity adds up. You hook up the batteries to accommodate the needs of the system.

Front 337

Charge controllers manage the interactions between what three things?

Back 337

1- the array
2- the battery bank
3- the loads

Front 338

Charge controllers are the heart of what?

Back 338

Stand-alone PV systems

Front 339

Charge controllers have a profound affect on what 3 things?

Back 339

1- on battery life
2- on load availability
3- on overall system performance

Front 340

Charge controllers _______ battery charging and protect batteries from ________.

Back 340

regulate
being over charged or over discharged

Front 341

Additional features may be incorporated in charge controllers to provide what?

Back 341

enhanced system control functions.

Front 342

Charge controllers use various _______ and _______ to manage battery state of charge.

Back 342

algorithms
switching designs

Front 343

________________ type charge controllers regulate charging current by switching it ON or OFF.

Back 343

Interrupting-

Front 344

____________ type charge controllers use a variable resistance to regulate charging current in a gradual manner.

Back 344

Linear-

Front 345

Shunt charge controllers control charging current by...

Back 345

short-circuiting the array

Front 346

Series charge controllers control charging current by...

Back 346

open-circuiting the array

Front 347

How does pulse-width modulation (PWM) simulate a variable current?

Back 347

by switching a full current ON and OFF at high speed for varying lengths of time.

Front 348

_________________ charge controllers divert the array current to an auxiliary load when the battery bank is fully charged.

Back 348

Diversionary

Front 349

_____________ setpoints are the battery conditions that trigger charge control actions.

Back 349

Charge controller

Front 350

_____________ setpoints determine when the array's charging current will be applied to the battery bank.

Back 350

Charge regulation

Front 351

_____________________ setpoints determine when the loads will be operating, preventing the battery bank from being overdischarged.

Back 351

Load control

Front 352

__________________ setpoints are determined by the charge control algorithm and type of battery.

Back 352

Optimal charge controller

Front 353

Setpoints should be adjusted for _____________ because ______________ affects battery charging characteristics.

Back 353

temperature
temperature

Front 354

Charge controllers must have the appropriate _________ and _____________ rating for the application requirements.

Back 354

voltage
current

Front 355

Long conductors between the charge controller and battery bank produce a voltage drop that affects the accuracy of what?

Back 355

the voltage measurement by the controller.

Front 356

Large arrays with multiple source circuits use ___________ for each circuit.

Back 356

individual charge controllers

Front 357

Multiple battery banks can be charged from one array with the use of either _______________ or _________________.

Back 357

multiple charge controllers
one specially configured charge controller.

Front 358

______________ PV systems do not require active charge control because the charging and discharging currents are carefully balanced.

Back 358

Self-regulating

Front 359

charge controller

Back 359

a device that regulates battery charge by controlling the charging voltage and/or current from a DC power source, such as a PV array.

Front 360

charge acceptance

Back 360

the ratio of the increase in battery charge to the amount of charge applied to the battery.

Front 361

overcharge

Back 361

the ratio of applied charge to the resulting increase in battery charge. It can also refer to the condition of a fully charged battery continuing to receive a significant charging current.

Front 362

deficit charge

Back 362

a charge cycle in which less charge is returned to a battery bank than what was withdrawn on discharge.

Front 363

overdischarge

Back 363

the condition of a battery state of charge declining to the point where it can no longer supply discharge current at a sufficient voltage without damaging the battery

Front 364

charge control algorithm

Back 364

a programmed series of functions that a charge controller uses to control current and/or voltage in order to maintain battery state of charge.

Front 365

interrupting-type charge controller

Back 365

a charge controller that switches the charging current ON and OFF for charge regulation.

Front 366

linear-type charge controller

Back 366

a charge controller that limits the charging current in a linear or gradual manner with high-speed switching or linear control

Front 367

shunt charge controller

Back 367

a charge controller that limits charging current to a battery system by short-circuiting the array

Front 368

shunt-interrupting charge controller

Back 368

a charge controller that suspends charging current to a battery system by completely short-circuiting the array

Front 369

shunt-linear charge controller

Back 369

a charge controller that limits charging current to a battery system by gradually lowering the resistance of a shunt element though which excess current flows.

Front 370

series charge controller

Back 370

a charge controller that limits charging current to a battery system by open-circuiting the array.

Front 371

series-interrupting charge controller

Back 371

a charge controller that completely open-circuits the array, suspending current flow into the battery.

Front 372

series-linear charge controller

Back 372

a charge controller that limits charging current to a battery system by gradually increasing the resistance of a series element.

Front 373

series-interrupting, pulse-width-modulated (PWM) charge controller

Back 373

a charge controller that simulates a variable charging current by switching a series element ON and OFF at high frequency and for variable lengths of time.

Front 374

maximum power point tracking (MPPT) charge controller

Back 374

a charge controller that operates the array at its maximum power point under a range of operating conditions, as well as regulates battery charging

Front 375

diversionary charge controller

Back 375

a charge controller that regulates charging current to a battery system by diverting excess power to an auxiliary load.

Front 376

diversion load

Back 376

an auxiliary load that is not a critical system load, but is always available to utilize the full array power in a useful way to protect a battery from overcharge

Front 377

hybrid system controller

Back 377

a controller with advanced features for managing multiple energy sources.

Front 378

ampere-hour integrating charge controller

Back 378

a charge controller that counts the total amount of charge (in ampere-hours) into and out of a battery and regulates charging current based on a preset amount of overcharge.

Front 379

charge controller setpoint

Back 379

a battery condition, commonly the voltage, at which a charge controller performs regulation or switching functions.

Front 380

voltage regulation (VR) setpoint

Back 380

the voltage that triggers the onset of battery charge regulation because it is the maximum voltage that a battery is allowed to reach under normal operating conditions.

Front 381

array reconnect voltage (ARV) setpoint

Back 381

the voltage at which an interrupting-type charge controller reconnects the array to the battery and resumes charging.

Front 382

voltage regulation hysteresis (VRH)

Back 382

the voltage difference between the voltage regulation (VR) setpoint and the array reconnect voltage (ARV) setpoint

Front 383

low-voltage disconnect (LVD) setpoint

Back 383

the voltage the triggers the disconnection of system loads to prevent battery overdischarge because it is the minimum voltage a battery is allowed to reach under normal operating conditions.

Front 384

load reconnect voltage (LRV) setpoint

Back 384

the voltage at which a charge controller reconnects loads to the battery system.

Front 385

low-voltage disconnect hysteresis (LVDH)

Back 385

the voltage difference between the low-voltage disconnect (LVD) and load reconnect voltage (LRV) setpoints.

Front 386

self-regulating PV system

Back 386

a type of stand-alone PV system that uses no active control systems to protect the battery, except through careful design and component sizing.

Front 387

What is the difference between charge acceptance and overcharge?

Back 387

Charge acceptance is the ration of increased battery charge to the amount of charge supplied to the battery. Overcharge is the ratio of applied charge to the resulting increase in battery charge. Overcharge is the inverse of charge acceptance.

Front 388

How do charge controllers protect battery banks from overcharge and overdischarge?

Back 388

A charge controller protects a battery from overcharge though regulation. This involves either interrupting or limiting the current flow from the array when the battery approaches a full state of charge. A charge controller protects a battery from overdischarge though load control, disconnecting electrical loads when the battery reaches a low voltage condition.

Front 389

Explain the differences between interrupting-type charge controllers and linear-type charge controllers.

Back 389

An interrupting-type charge controller switches the charging current ON and OFF for charge regulation. They have a simple design, but are not widely used since the array current is switched abruptly which makes it difficult to avoid excessive overcharges. A linear-type charge controller limits the charging current in a gradual manner with high-speed switching or linear control. They provide a more consistent charging process that is more efficient, faster, and compatible with most types of batteries.

Front 390

Explain the differences between shunt and series charge controllers.

Back 390

A shunt charge controller is a charge controller that limits charging current to a battery system by short-circuiting the array. The array is short-circuited though a shunt element inside the charge controller, moving the operating point on the I-V curve very near the short-circuit condition and limiting the power output. A blocking diode is needed to keep the battery from short circuiting. A series charge controller limits charging current to a battery system by open-circuiting the array. As the battery reaches full state of charge, a switching element inside the controller opens, moving the arrays operating point on the I-V curve to the open-circuit condition and limiting the power output. No blocking diode is needed. This method works in series between the array and battery, rather than in parallel as for the shunt controller.

Front 391

How does PWM technology regulate charging current?

Back 391

A PWM charge controller pulses the full charging current and varies the width of the pulses to regulate the amount of charge current flowing into the battery. When the battery is partially charged, the current pulse is essentially ON all the time. To simulate a lower charging current as the voltage rises, the pulse width is decreased.

Front 392

How does a diversionary charge controller utilize excess energy?

Back 392

by diverting excess power to an auxiliary load. Instead of wasting excess power, the auxiliary load provides a useful output with the diverted power. Examples of diversion loads include loads with inherent energy storage, such as resistance water heaters, ventilation fans, and irrigation pumps. The NEC requires a secondary, independent means of charge control (usually a series controller) when diversionary charge control is used.

Front 393

Explain four primary charge controller setpoints.

Back 393

1- (VR) the voltage regulation setpoint is the voltage that triggers the onset of battery charge regulation.
2- (ARV) the array reconnect voltage setpoint is the voltage at which a charge controller reconnects the array to the battery and resumes charging.
3- (LVD) the low-voltage disconnect setpoint is the voltage that triggers the disconnection of system loads to prevent battery overdischarge.
4- (LRV) the load reconnect voltage setpoint is the voltage at which a charge controller reconnects loads to the battery system.

Front 394

What are the possible consequence of a charge controller hysteresis that is too narrow or too large?

Back 394

If the voltage regulation hysteresis (VRH) is too large, the array current remains disconnected for long periods, wasting energy from the array and making it difficult to fully charge the battery. If the VRH is too small, the array will cycle ON and OFF rapidly, which limits the life of switching elements.
If the low-voltage disconnect hysteresis (LVDH) is too small, the load may cycle ON and OFF rapidly at low battery state of charge, possible damaging the load or control elements, and extending the time it takes to fully charge the battery. If the LVDH is too large, the load may remain OFF for extended periods while the array more fully charges the battery. The reduced cycling improves battery health, but also limits load availability during low insolation periods.

Front 395

Why must charge controller setpoints be temperature-compensated?

Back 395

Temperature affects battery charging characteristics, so some charge controllers adjust setpoints to compensate for this factor. When battery temperature is low temperature compensation increases the VR setpoint to allow the battery to reach a moderate gassing level and fully charge. When temperature is high, the VR setpoint is lowered to minimize excessive overcharge and electrolyte loss. Temperature compensation helps ensure that a battery is fully charged during cold weather and not overcharged during hot weather.

Front 396

How does the distance between the charge controller and battery bank affect the regulation functions of a charge controller?

Back 396

Since many charge controllers sense battery voltage with the conductors used to deliver charging current, the measured voltage is slightly higher than the actual battery voltage (due to voltage drop). This prematurely activates charge regulation, causing the battery to be undercharged. Excessive voltage drop also affects the load control setpoints. The discharge current causes the measured voltage from the charge controller to be lower than the actual battery voltage. This results in the loads being disconnected at an actual battery voltage that is slightly higher than the LVD setpoint. The voltage drop during charging and discharging effectively compresses the actual operating voltage range of the battery, reducing the available battery capacity.

Front 397

How do low-voltage modules control charging current?

Back 397

Low-voltage modules take advantage of the fact that the module current falls off sharply as the voltage increases above the maximum power point. By matching the maximum power voltage with the battery charge regulation voltage, charge current is naturally limited as the battery approaches full state of charge, helping prevent battery overcharge.

Front 398

Name 3 common AC waveforms produced by inverters.

Back 398

1- sine waves
2- square waves
3- modified square waves

Front 399

Why do some AC inverters bother with producing square or modified square waves? Why don't they just produce sine waves?

Back 399

Sine waves are the most complicated type of AC waveform for inverters to produce, so some less-sophisticated inverters approximate the sine wave with square waves or modified square waves.

Front 400

____________ inverters change DC power to AC power using electronics, so they have no moving parts and are very efficient.

Back 400

Static (solid-state)

Front 401

____________ inverters are small inverters that take the place of a DC junction box on a PV module.

Back 401

AC module

Front 402

Inverters use _______ and _________ to switch DC power and produce AC power.

Back 402

thyristors
transistors

Front 403

____________ inverters use an external signal to control the switching devices, while ______________ inverters include microprocessors for precise timing and control of the switching devices.

Back 403

Line-commutated
Self-commutated

Front 404

How does a square wave become a modified square wave?

Back 404

by adjusting the duration of the alternating pulses

Front 405

______________ is used to construct the closest approximation of a sine wave.

Back 405

Pulse-width modulation (PWM)

Front 406

____________________ perform one or more power processing and control functions in addition to inverting.

Back 406

Power conditioning units

Front 407

Name 4 power processing and control functions that may be done in addition to inverting by a power conditioning unit.

Back 407

1- rectification
2- transformation
3- DC-DC conversion
4- maximum power point tracking

Front 408

Name 4 things that transformers can be used for.

Back 408

1- to convert between high and low AC voltages
2- to change impedance
3- to provide electrical isolation
4- to regulate voltage

Front 409

The principal inverter specification is the ________ rating.

Back 409

power

Front 410

____________ is the primary limiting factor for inverter power ratings.

Back 410

temperature

Front 411

DC input voltage ratings are based on the operating characteristics of either a _________ or a __________.

Back 411

battery bank (for stand-alone inverters)
PV array (for interactive inverters)

Front 412

Operating and maximum allowable AC and DC current ratings are determined by the ______________ capabilities of switching devices used in the inverter.

Back 412

current-handling

Front 413

Most inverters include features to protect the inverter and connected equipment from damage caused by what 3 things?

Back 413

1- excessive temperatures
2- excessive currents
3- excessive power levels

Front 414

Direct current (DC)

Back 414

electrical current that flows in one direction, either positive or negative.

Front 415

Alternating current (AC)

Back 415

electrical current that changes between positive and negative directions

Front 416

waveform

Back 416

the shape of an electrical signal that varies over time.

Front 417

periodic waveform

Back 417

a waveform that repeats the same pattern at regular intervals

Front 418

cycle

Back 418

the interval of time between the beginnings of each waveform pattern

Front 419

sine wave

Back 419

a periodic waveform the value of which varies over time according to the trigonometric sine function.

Front 420

sinusoidal waveform

Back 420

a waveform that is or closely approximates a sine wave

Front 421

square wave

Back 421

an alternating current waveform that switches between maximum positive and negative values every half period

Front 422

modified square wave

Back 422

a synthesized, stepped waveform that approximates a true sine wave.

Front 423

frequency

Back 423

the number of waveform cycles in one second.

Front 424

period

Back 424

the time it takes a periodic waveform to complete one full cycle before it repeats

Front 425

peak

Back 425

the maximum absolute value of a waveform

Front 426

peak-to-peak

Back 426

a measure of the difference between positive and negative maximum values of a waveform

Front 427

root-mean-square (RMS) value

Back 427

a statistical parameter representing the effective value of a waveform.

Front 428

power quality

Back 428

the measure of how closely the power in an electrical circuit matches the nominal values for parameters such as voltage, current, harmonics, and power factor.

Front 429

voltage unbalance

Back 429

the unbalance that occurs when the voltages of a three-phase power supply or the terminals of a three-phase load are not equal.

Front 430

single phasing

Back 430

the complete loss of one phase on a three-phase power supply

Front 431

current unbalance

Back 431

the unbalance that occurs when current is not equal on the three power lines of a three-phase system

Front 432

phase unbalance

Back 432

the unbalance that occurs when three-phase power lines are more or less than 120 degrees out of phase

Front 433

harmonic

Back 433

a waveform component at an integer multiple of the fundamental waveform frequency.

Front 434

total harmonic distortion (THD)

Back 434

the ratio of the sum of all harmonic components in a waveform to the fundamental frequency component.

Front 435

resistive load

Back 435

a load that keeps voltage and current waveforms in phase

Front 436

true power

Back 436

the product on in-phase voltage and current waveforms and produces useful work

Front 437

reactive load

Back 437

an AC load with inductive and/or capacitive elements that cause the current and voltage waveforms to become out of phase.

Front 438

reactive power

Back 438

the product of out-of-phase voltage and current waveforms and results in no net power flow

Front 439

power factor

Back 439

the ratio of true power to apparent power and describes the displacement of voltage and current waveforms in AC circuits.

Front 440

apparent power

Back 440

a combination of true and reactive power and is given in units of volt-amperes (VA)

Front 441

inverter

Back 441

a device that converts DC power to AC power

Front 442

AC module

Back 442

a PV module that outputs AC power through an interactive inverter attached in place of the normal DC junction box.

Front 443

line-commutated inverter

Back 443

an inverter whose switching devices are triggered by an external source.

Front 444

self-commutated inverter

Back 444

an inverter that can internally control the activation and duration of its switching.

Front 445

H-bridge inverter circuit

Back 445

a circuit that switches DC input into square wave AC output by using two pairs of switching devices.

Front 446

push-pull inverter circuit

Back 446

a circuit that switches DC input into AC output by using one pair of switching devices and a center-tapped transformer

Front 447

pulse-width modulation (PWM)

Back 447

a method of simulating waveforms by switching a series device ON and OFF at high frequency and for variable lengths of time.

Front 448

rectifier

Back 448

a device that converts AC power to DC power

Front 449

transformer

Back 449

a device that transfers energy from one circuit to another through magnetic coupling

Front 450

DC-DC converter

Back 450

a device that changes DC power from one voltage to another

Front 451

maximum power point tracker (MPPT)

Back 451

a device or circuit that uses electronics to continually adjust the load on a PV device under changing temperature and irradiance conditions to keep it operating at its maximum power point

Front 452

inverter efficiency

Back 452

the effectiveness of an inverter at converting DC power to AC power

Front 453

stand-by losses

Back 453

the power required to operate inverter electronics and keep the inverter in a powered state.

Front 454

Why is sine wave output the preferred inverter output?

Back 454

The rotating generators that provide most of the electrical power on the utility grid naturally produce sine waves, so most loads are designed to operate using sinusoidal AC power. Therefore, interactive inverters produce sine waves for utility synchronization. Other waveforms may damage some loads.

Front 455

How do modified square wave inverters compare with square wave inverters in terms of power quality? Specifically, what are the 4 advantages of a modified square wave over a simple square wave?

Back 455

In terms of power quality, a modified square wave is a substantial improvement over a simple square wave.
Compared to square wave inverters, modified square waver inverters have:
1- lower harmonic distortion,
2-higher peak voltage,
3-higher efficiency, and
4-better surge current capability.

Front 456

How is power quality relevant to inverter output?

Back 456

Power quality problems can be caused by the power source, but they can also be caused by loads on the electrical system. It is important to ensure adequate power quality in inverter systems, as in any electrical system. Most inverters perform much of the power quality monitoring automatically, so problems usually are easy to identify. Harmonics are present in square waves and modified square waves, so harmonics issues are especially important for inverters producing these types of waveforms.

Front 457

Compare the basic system configurations of stand-alone, interactive and bimodal inverters.

Back 457

Stand-alone inverters are connected to the battery bank and supply AC power to a distribution panel that is independent of the utility grid. Utility-interactive inverters are connected to, and operate in parallel with, the electric utility grid. Bimodal inverters can operate in either interactive or stand-alone mode (not simultaneously).

Front 458

What are the similarities and differences between thyristors and transistors?

Back 458

Thyristors and transistors are solid-state electronic components used in inverters. Both types of components perform switching functions when activated by a control signal. However, thyristors are activated by a small current, while transistors are activated by a small voltage. Also, thyristors can be only completely ON or completely OFF, while transistors can be activated by any degree in between, like a dimmer switch.

Front 459

Why can line-commutated inverters not be used in stand-alone systems?

Back 459

Line-commutated inverters alternately turn the switches ON and OFF by the positive and negative half-cycles of the utility voltage, automatically synchronizing the inverter output to the utility. Therefore, since stand-alone systems do not use the utility (or an outside AC signal for that matter), they cannot operate independently of the grid.

Front 460

How does higher-frequency control result in better approximation of a true sine wave?

Back 460

Pulse-width modulation (PWM) simulates waveforms by switching a series device ON and OFF at high frequency and for variable lengths of time. When the pulses are narrow, the current id OFF most of the time, which simulates a low voltage. When pulses are wide, the current is ON most of the time, which simulates a high voltage. By using very high frequencies and gradual changes in pulse width, the PWM output appears to be a smooth, true sine wave.

Front 461

How are inverters different from power conditioning units?

Back 461

The physical enclosure that is referred to as an inverter is actually often a power conditioning unit (PCU). Power conditioning units perform one or more power processing and control functions in addition to inverting.

Front 462

Why is it important for inverters to manage their temperature?

Back 462

Solid-state switching devices are capable of handling only so much current before they become overheated and fail. Therefore, thermal management in electronic inverters is a major concern, and temperature is the primary limiting factor for inverter power ratings. Many inverters use heat sinks and/or ventilation fans to regulate temperature. Interactive inverters control high temperatures by forcing a higher DC input voltage, which reduces the input current.

Front 463

How do stand-by losses affect inverter efficiency for various power levels?

Back 463

Stand-by losses are the power required to operate inverter electronics and keep the inverter in a powered state. Inverter stand-by losses are nearly constant for all output power levels, so efficiency is lower for low power outputs.

Front 464

What types of system operating information are typically provided by inverter interfaces?

Back 464

Most modern inverters provide features for data monitoring and communications. Interfaces may include displays and controls on the inverter itself, while others interface with remote units or computers. Inverter interfaces typically provide basic system information, including interconnection status, AC output voltage and power, DC input voltage, MPPT status, error codes, fault conditions, and other parameters. Many inverters record energy production on daily and cumulative bases.

Front 465

Sizing analysis for stand-alone systems starts at the ________ side and proceeds backwards to the ______.

Back 465

load
array

Front 466

Why are interactive systems generally sized to be as large as possible within the limits of available space and budget?

Back 466

In most locations, occasional excess energy can be sold back to the utility.

Front 467

Sizing of stand-alone systems involves a fine balance between ___________ and _____________.

Back 467

energy supply
energy demand

Front 468

In a stand-alone system, what would be the consequence of sizing the system too small?

Back 468

If the system is too small, there will be losses in load availability and system reliability.

Front 469

In a stand-alone system, what would be the consequence of sizing the system too large?

Back 469

If the system is too large, excess energy will be unutilized and wasted.

Front 470

Bimodal systems are typically sized in the same was as _____________ systems.

Back 470

stand-alone

Front 471

The PV array and battery bank in a hybrid system can be significantly smaller than in a stand-alone system if...

Back 471

the secondary power source is available on demand.

Front 472

A detailed load analysis completed during the site survey lists what 3 things?

Back 472

1- each load
2- each loads power demand
3- the daily energy consumption

Front 473

A ______________ operating time accounts for multiple loads operating for varying lengths of time per day.

Back 473

weighted average

Front 474

Why does it require more DC energy to produce a certain amount of AC energy?

Back 474

Because inverters lose some power in the process of converting DC energy to AC energy.

Front 475

Why are stand alone systems sized for the worst-case scenario of high load and low isolation?

Back 475

because a stand-alone system must produce enough electricity to meet load requirements during any month.

Front 476

If the load requirements vary from month to month, the critical design month may turn out to be...

Back 476

any month of the year.

Front 477

The highest critical design ratio in each orientation corresponds to what?
When multiple orientations are considered, the lowest ratio of the resulting critical design months corresponds to what?

Back 477

to the critical design month for that orientation.

to the optimal array orientation (of the orientations analyzed)

Front 478

The DC voltage for battery-based PV systems is usually an integer multiple of ____ volts, usually _______, __________, or _________.

Back 478

12
12V
24V
48V

Front 479

Noncritical systems are typically designed for _______ to _________ days autonomy, critical systems are typically designed for ______ to ________ days of autonomy or more.

Back 479

3
5
6
10

Front 480

Why must the ratings of battery banks be higher than the required battery-bank output?

Back 480

because several factors reduce the useful capacity of a battery.

Front 481

The __________ and ________ of the selected battery are used to determine the configuration of the battery bank.

Back 481

nominal voltage
rated capacity

Front 482

Why must the array ratings be higher than the required array output?

Back 482

Like batteries, several factors reduce the output of a PV module.

Front 483

Why is it impractical from an economic standpoint to make a PV system significantly larger than needed for all but the most critical applications?

Back 483

because each percentage-point increase in system availability costs increasingly more money for larger battery banks and arrays.

Front 484

Duty cycle

Back 484

the percentage of time a load is operating

Front 485

critical design ratio

Back 485

the ratio of electrical energy demand to average insolation during a period

Front 486

critical design month

Back 486

the month with the highest critical design ratio

Front 487

system availability

Back 487

the percentage of time over an average year that a stand-alone PV system meets the system meets the system load requirements

Front 488

autonomy

Back 488

the amount of time a fully charge battery system can supply power to system loads without further charging.

Front 489

load function

Back 489

the portion of load operating power that comes from the battery bank over the course of a day.

Front 490

soiling

Back 490

the accumulation of dust and dirt on an array surface that shades the array and reduces electrical output.

Front 491

What is involved in sizing interactive systems?
Name the four primary steps in order.

Back 491

When sizing a PV system it is necessary to consider the energy demand before considering the supply. Therefore, PV-system sizing, particularly for stand-alone systems, starts at the load side and proceeds backward to the array.
1-determine the requirements of the system loads
2-determine the size of the inverter
3- determine the size of the battery bank
4- determine the size of the array that is needed to meet the requirements.

Front 492

Why does the sizing of a stand-alone system require critical calculations and tight tolerances?

Back 492

Stand-alone PV systems are designed to power specific on-site loads, so the size of these systems is directly proportional to the load requirements. If the system is too small, there will be losses in load availability and system reliability. If the system is too large, excess energy will be unutilized and wasted. Therefore, sizing of stand-alone systems requires a fine balance between energy supply and demand.

Front 493

What methodology is used to size bimodal systems?

Back 493

Bimodal systems normally operate as interactive systems, but can operate as stand-alone systems during utility outages. Therefore, the bimodal systems are typically sized according to the stand-alone methodology. However, a significant difference between bimodal systems and true stand-alone systems is that bimodal systems typically supply only a few select critical loads while in stand -alone mode.

Front 494

Explain three differences between sizing a stand-alone system and sizing the PV portion of a PV array and engine generator hybrid system.

Back 494

1- the array is sized to supply only a portion of the total load requirement in a hybrid system.
2- the sizing calculations do not need to use the worst-case load-to-insolation months for sizing, since the engine generator can be called upon to provide additional power as needed.
3- battery banks can be sized for a shorter autonomy period (usually 1 or 2 days) than for PV-only stand-alone systems (generator is available on demand)

Front 495

Describe the basic analysis procedure for sizing a stand-alone system. (four steps)

Back 495

1- a load analysis determines the electrical load requirements
2- monthly load requirements are compared to the local insolation data to determine the critical design parameters
3- the battery bank is sized to be able to independently supply the loads for a length of time if cloudy weather reduces array output.
4- the PV array is sized to fully charge the battery bank according to the critical design parameters.

Front 496

Why must AC loads and DC loads be listed separately in a load analysis?

Back 496

This is because energy for AC loads goes through the inverter, resulting in losses that must be accounted for separately.

Front 497

What 4 factors are involved in inverter selection?

Back 497

1-The inverter must have a maximum continuous power output rating at least as great as the largest single AC load
2- it must be able to supply surge currents.
3- The voltage output. Most stand-alone inverters produce either 120V single phase or 120/240V split-phase output. Some higher-power inverters output three phase power.
4-The inverter DC-input voltage must also correspond with either the array voltage (for interactive systems) or the battery-bank voltage (for stand alone systems)

Front 498

How does sizing for the critical design month improve system availability?

Back 498

It helps to ensure that a stand-alone system will produce enough electricity to meet load requirements during any month. Systems are sized for the worst-case scenario of high load and low insolation. A critical design analysis compares these two factors throughout a year, and the data for the worst-case is used to size the array.

Front 499

How does system availability affect system cost?

Back 499

Most stand-alone systems are sized for a system availability up to about 95% for noncritical applications and to 99% or greater for critical applications. Each percentage-point increase in system availability costs is increasingly more expensive for larger battery banks and arrays, which is impractical from an economic standpoint for all but the most critical applications. Sizing of stand-alone systems must achieve an acceptable balance between system availability and cost goals for a given application.

Front 500

What three factors affect the required rating of the battery bank in relation to the required battery-bank output?

Back 500

1- The amount of discharge allowed on a battery to avoid damage (about 80% discharge)
2- The battery operating temperature (low temps reduce capacity)
3- The rate of battery discharge (high discharge rates reduce capacity)

Most batteries cannot be discharged to a depth of 100% without permanent damage. Depending on The battery type, common allowable depths of discharge range from 20% to 80%. Most PV systems use deep-cycle lead-acid batteries, which can be discharged to about 80%. Low operating temperatures and high discharge rates further reduce battery capacity. Most battery ratings are for operation at 77 F and at a certain discharge rate. Temperatures below this and discharge rates above average will lower battery capacity.

Front 501

What three factors are used to determine the required voltage and current rating of the array from the required array voltage and current outputs?

Back 501

Just as with battery banks, certain factors reduce the array output from the factory ratings to actual output values.
1- Array current output is reduced when dust and debris collect on the array surface, blocking solar radiation.
2- High temperature reduces voltage output.
3- The necessary voltage increase in order to charge the batteries.

Front 502

Existing structures should be evaluated for structural ___________ before installing an array.

Back 502

soundness

Front 503

Good access to the array mounting location makes installation.... (4)

Back 503

safer, easier, faster, and less expensive.

Front 504

Only passive cooling means are practical for flat-plate modules, such as....

Back 504

mounting in a way to allow air circulation around the modules

Front 505

Arrays mounted directly on building surfaces can increase what?

Back 505

heat transfer into conditioned spaces

Front 506

Arrays mounted above building surfaces have little effect on building __________ and may even help reduce interior building _______.

Back 506

heat gain
temperatures.

Front 507

Architectural principles that can improve appearance and public perception can be applied to PV system design and installation without significantly affecting ___________ or ____________.

Back 507

cost
performance

Front 508

Name 5 things that should be mounted as inconspicuously as possible when installing a PV array.

Back 508

1- array support structures
2- hardware
3- electrical wiring (neatly gathered and concealed)
4- conduit
5- junction boxes

Front 509

Reducing installation time though careful preparation can significantly reduce _________.

Back 509

costs

Front 510

The simplest and most common type of array mount is the ___________ type.

Back 510

fixed-tilt

Front 511

Rack mounts are ___________ to install and ______ in the types and sizes of modules they can accommodate.

Back 511

simple
flexible

Front 512

______________ arrays are by far the most common, preferred, and least-expensive method for installing arrays as a retrofit to existing rooftops, as well as for new construction.

Back 512

Standoff-mounted

Front 513

_____________ arrays can be integrated into roofing, windows, skylights, curtain wall sections, or complementary architectural features such as awnings, facades, or entranceways.

Back 513

Building-integrated photovoltaic (BIPV)

Front 514

_______________ arrays are generally more flexible in location and placement, operate at lower temperatures than most building mounts, and are more accessible.

Back 514

Ground-mounted

Front 515

___________ arrays can follow the sun, enhancing the amount of energy collected, but are also complex and require more expense and installation time.

Back 515

Sun-tracking

Front 516

___________ construction is generally avoided in PV system installation

Back 516

wood

Front 517

What 3 types of materials are commonly used for parts and fasteners in array designs because they are corrosion resistant, lightweight, and relatively inexpensive?

Back 517

1- aluminum
2- stainless steel
3- galvanized steel

Front 518

Arrays, modules, mounting systems, fasteners, and buildings must withstand the maximum ______ expected from structural loads.

Back 518

forces

Front 519

Name the 5 principal types of structural loads.

Back 519

1- dead loads
2- live loads
3- wind loads
4- snow loads
5- vibration loads

Front 520

Most attachment methods use conventional ____________ fasteners and screws.

Back 520

threaded

Front 521

_________ and ___________ techniques can be used to support bolted attachment points.

Back 521

blocking
spanning

Front 522

______________ systems do not require direct structural connections to a building or foundation.

Back 522

Self-ballasted

Front 523

List the two different common methods for installing poles.

Back 523

1- embedded in concrete or compacted soil
2- twisted into the ground like giant screws

Front 524

___________ of structural attachments and roof penetrations is a major concern for building-mounted arrays.

Back 524

weather sealing

Front 525

The number of roof penetrations should be ____________.

Back 525

minimized

Front 526

installed nominal operating cell temperature (INOCT)

Back 526

the estimated temperature of a module operating in a specific mounting system design.

Front 527

fixed-tilt mounting system

Back 527

an array mounting system that permanently secures modules in a non-moveable position at a specific tilt angle.

Front 528

adjustable mounting system

Back 528

a variation of a fixed-tilt mounting system that permits manual adjustment of the tilt and/or azimuth angles to increase the array output.

Front 529

direct mount

Back 529

a type of fixed-tilt array mounting system where modules are affixed directly to an existing finished rooftop or other building surface, with little or no space between a module and the surface.

Front 530

rack mount

Back 530

a type of fixed-or adjustable-tilt array mounting system with a triangular-shaped structure to increase the tilt angle of the array.

Front 531

standoff mount

Back 531

a type of fixed-tilt array mounting system where modules are supported by a structure parallel to and slightly above the roof surface.

Front 532

building-integrated photovoltaic (BIPV) array

Back 532

a fixed array that replaces conventional building materials with specially designed modules that perform an architectural function in addition to producing power.

Front 533

pole mount

Back 533

a type of array mounting system where modules are installed at an elevation on a pedestal

Front 534

sun-tracking mount

Back 534

an array mounting system that automatically orients the array to the position of the sun.

Front 535

active tracking mount

Back 535

an array mounting system that uses electric motors and gear drives to automatically direct the array toward the sun.

Front 536

passive tracking mount

Back 536

an array mounting system that uses nonelectrical means to automatically direct an array toward the sun.

Front 537

galvanic corrosion

Back 537

an electrochemical process that causes electrical current to flow between two dissimilar metals, which eventually corrodes one of the materials (the anode)

Front 538

sacrificial anode

Back 538

a metal part, usually zinc or magnesium, that is more susceptible to galvanic corrosion than the metal structure it is attached to, so that it corrodes, rather than the structure.

Front 539

design load

Back 539

a calculated structural load used to evaluate the strength of a structure to failure

Front 540

dead load

Back 540

a static structural load due to the weight of permanent building members, supported structure, and attachments.

Front 541

live load

Back 541

a dynamic structural load due to the weight of temporary items and people using or occupying the structure.

Front 542

wind load

Back 542

a dynamic structural load due to wind, resulting in downward, lateral, or lifting forces.

Front 543

basic wind speed

Back 543

the maximum value of a 3 second gust at 33' elevation, which is used in wind load calculations

Front 544

exposure

Back 544

a wind load factor that accounts for the array height and the characteristics of the surrounding terrain

Front 545

snow load

Back 545

a static structural load due to the weight of accumulated snow.

Front 546

vibration load

Back 546

a dynamic structural load due to periodic motion

Front 547

resonance

Back 547

the condition when a vibration frequency matches the fundamental frequency of the structure.

Front 548

allowable withdrawal load

Back 548

the force required to remove a screw from a material by tensile (pulling) force only.

Front 549

blocking

Back 549

the addition of lumber under a roof surface and between trusses or rafters as supplemental structural support.

Front 550

spanning

Back 550

the addition of lumber under a roof surface and across trusses or rafters as supplemental structural support

Front 551

J-bolt

Back 551

a fastener that hooks around a secure support structure and has a threaded end that is used with a nut to secure items.

Front 552

self-ballasting

Back 552

an attachment method that relies on the weight of the array, support structure, and ballasting material to hold the array in position.

Front 553

How can mechanical integration strategies help keep arrays cool?

Back 553

Cooler arrays generally are more reliable, last longer, operate with greater efficiency, and produce more power, so array temperatures should be minimized wherever possible. Active cooling means, such as fans and water-circulating pumps, may be used with some concentrating arrays, but are not practical for flat-plate modules. Only passive cooling means are employed for flat-plate modules, such as mounting the array in a way that allows air circulation around the modules. Keeping modules and arrays clear of obstructions also promotes natural cooling.

Front 554

How can direct-mounted and standoff-mounted arrays affect the temperatures inside a building?

Back 554

Some arrays (direct-mounted) radiate additional heat into a building. The array absorbs heat energy from direct radiation and conducts it through the roofing materials to the underside of the roof surface. There the energy heats the interior spaces of the building.
Conversely, arrays mounted above the building surfaces (standoff-mounted) have little effect on building heat gain, or may even reduce interior building temperatures. These modules shade part of the roof from direct radiation, while the space between the modules and the roof surface keeps the modules from transferring much heat to the roof and allows wind to cool the roof surface.

Front 555

What are some of the aesthetic considerations of mechanical integration?

Back 555

While the outward appearance of arrays and overall installations has little to do with system functionality or performance, it has a notable influence on consumer acceptance of PV technology. For arrays mounted on sloped roofs, the lines and location of the array should be consistent with building features. Color may be a consideration in choosing and integrating modules to complement other building colors. Finally, quality workmanship on the overall system installation improves the aesthetic appearance.

Front 556

How does the distance between modules and a building surface affect the module's installed nominal operating cell temperature (INOCT) and temperature-rise coefficient?

Back 556

Standoff mounts allow air to circulate beneath the array, keeping modules cool and reducing heat gain into buildings. INOCT for standoff arrays is a function of the standoff height. Standoff heights from 1" to 3" have a high INOCT, from 3" to 6" the INOCT is somewhat cooler, and standoff heights above 6" have the lowest INOCT for standoff arrays.

Front 557

Explain how building-integrated PV (BIPV) arrays offset some building material costs.

Back 557

A BIPV array replaces some conventional building materials with modules that also perform a structural or cladding function. BIPV windows, skylights, awnings, and facades. The cost of the array is partially offset by avoiding the cost of some of the conventional building materials, though high engineering and architectural costs often outweigh the savings.

Front 558

How do sun-tracking systems improve the power output of a PV system?

Back 558

A sun-tracking mount is an array mounting system that automatically orients the array to the position of the sun. This can increase annual solar gain by as much as 40% in some areas when compared to a fixed-tilt mounting design.

Front 559

What factors influence the added value of a sun-tracking mounting system?

Back 559

Sun-tracking arrays increase the array's power output, but are complex systems and require a greater investment in time and expense. In order for active tracking mounts to be effective, the solar energy gained by tracking must more than compensate for the electrical energy used by active tracking motors. The energy gain must also offset the increased maintenance and troubleshooting likely with these systems.

Front 560

Why do the aluminum materials common in module frames present a corrosion problem when installed on steel structures?

Back 560

Galvanic corrosion results from direct contact of dissimilar metals. Galvanic corrosion is an electrochemical process that causes electrical current to flow between two dissimilar metals which eventually corrodes one of the material (the anode). The rate of corrosion depends on the properties of the two metals in contact, as well as temperature and humidity. Aluminum (module frames) and steel (mounting structures) combinations are particularly prone to galvanic corrosion. This can be mitigated by electrically insulating the metals with rubber or fiber material or by adding sacrificial anodes.

Front 561

Explain the difference between static and dynamic structural loads and classify the principal types of structural loads as static or dynamic.

Back 561

The principal types of structural loads are dead loads, live loads, wind loads, snow loads, and vibration loads. These loads are either static or dynamic. Static loads are constant loads, while dynamic loads change in magnitude and sometimes in direction. Dead loads and snow loads are static loads. Live loads, wind loads, and vibration are dynamic loads.

Front 562

Explain the three primary factors that influence wind loads for most PV applications.

Back 562

For most PV system applications, three primary factors influence wind loads:
1- wind speed: The maximum value of a 3 second gust at 33' elevation. The local building code authority may provide this information, or it may be determined from a map.
2- exposure: a wind load factor that accounts for the array height and the characteristics of the surrounding terrain. More obstructions to wind, less exposure.
3- array tilt: The tilt angle of a surface greatly affects potential wind loads. Wind loads are small for array tilt angles around 20 degrees, and increase with larger tilt angles up to 90 degrees. Also low tilt angles of 10-15 degrees may act as an airfoil and increase wind loads.

Front 563

How can lag-screw attachment points be supported when they do not match rafter locations?

Back 563

Lag screws must be secured into thick, solid pieces of wood, such as rafters. When attachment points must be made where there are no rafters underneath, doubled-up blocking can be used. Blocking is the addition of lumber under a roof surface and between trusses or rafters as supplemental structural support.

Front 564

Describe the advantages and disadvantages of self-ballasted systems.

Back 564

Self-ballasting is an attachment method that relies on the weight of the array, support structure, and ballasting material to hold the array in position. Self-ballasted systems do not require direct structural connections with fasteners to a building or foundation. A major advantage of these systems is that there are no penetrations into the building surfaces, eliminating concerns about weather sealing of attachment points. They are also installed very quickly and use fewer fasteners. However, self-ballasted systems must be installed on level surfaces an may be limited to regions without high basic wind speeds.